Study on Dual-Energy X-ray Computed Tomography using Synchrotron Radiation

The electron density is one of the most important element for thetreatment planning in the radiotherapy, because this information isused for the range estimation of the heavy-ion beam. Although theelectron density has been converted from CT number obtained byconventional x-ray computed tomography(CT) at present, it is notenough for the more detailed planning due to uncertainties that arisefrom the beam hardening effect and the conversion process. In order totake more accurate electron density, we have developed the dual-energyx-ray CT system using the synchrotron radiation. The dual-energy x-rayCT has no influence of the beam hardening because of scanning usingmonochromatic x-rays. The experiments were carried out using twomonochromatic x-rays at the monochromatic beam-lines in KEK-AR andSPring-8. As the result, it was succeeded that the electron densitiesby the dual-energy x-ray CT were agreement with the theoretical valueswith the accuracy less than 1% for some materials. In addition, as theapplication for more practical use in diagnostics, the CT using themixture of main and harmonics x-rays produced by the monochromator hasbeen investigated. From the preliminary experiments, it was found thatthe accuracy was as same as that by dual-energy x-ray CT. We willdescribe the dual-energy x-ray CT system and discuss thequantitativity and the image characteristic for this system.Eighth International Conference on Synchrotron Radiation Instrumentatio

Development of Dual-Energy X-ray CT using Synchrotron Radiation

Monochromatic x-ray CT at two different energies provides information about electron density without ambiguity due to the beam hardening effect. This information makes the treatment planning for heavy-ion radiotherapy more precise. We have started a feasibility study on the dual-energy x-ray CT by using synchrotron radiation. We developed a linear scanning CT system(1D-CT) in order to evaluate what precision in the measurement was achieved. Comparison fo measured electron densities with the theoretical values proved that these values were in afreement in 0.9 % on average. We haave developed a 2D-CT system with a two-dimensional scintillator array to take images in a short time. At present, it has been proved that the electron density is measured in the precision of about 1 %. Effectove atomic numbers are obtained as well from the dual-energy x-ray CT. They present a different feature of an object, and the contrasts in the images differ from that in a conventional CT image. The feature of the images may help distinguish more clearly tissues or organs with aid of difference contrast from the conventional CT images.International Symposium on Portable Synchrotron Light Sources and Advanced Application